upgrade path from my current speakers? (Dynaudio Special Forty)

Sounds like the DynAudio is the place to start. Sounds like you are doing fairly fast semirandom equipment swapping. That makes getting where you want to go nearly impossible. You need to start with a good set of speakers and then upgrade the electronics and room treatments to support them. If we can see the room it would be helpful. 
 

Definitely a bluesound streamer is a very weak point. But it is important to carefully choose each component to take advantage of your speakers and push the sound quality to your tastes.

Multiple Youtube reviewers, including Steve Guttenberg, tout the Buchardt S400 MK II  as a world beating stand mount speaker in the same class as Dynaudio, but here it is rarely mentioned.  Any ideas?

@kb54 your question seems like a separate topic but I think the reason Buchardt isn’t heavily mentioned on Audiogon is that they are a newer manufacturer and Audiogon’s members are older and tend to focus on more established brands. Most of the Buchardt hype is coming from the youtube reviewer community, which draws newer audiophiles.

Personally I’m not a fan of investing in companies that are quick to revise or push out new models. It's bad for resale. Their lineup is a bit of a mess, just looking at passive models they went from S300>S400>S300mk2>S400mk2 and then a low cost P300 which I’m assuming will retire the S300 series altogether. All in under 10 years. And I’m not including SE versions with custom finishes & wiring. To me that feels like they are taking their customers for a ride.

Regarding Buchardts, I have owned the s400 and now own the 400SE. There is a clear difference in the sound between the two. The 400 is a warmish-sounding speaker, whereas the 400SE is more neutral. The 400 has a laid-back treble the SE is more forward in the treble. That is the most notable difference The Speical 40 IMO is better sounding than both. The 40 is more energetic and punchy in the bass. Having said that, the Buchardts are very good sounding for the money. They do not need as much power to sound their best as the 40's.

Revival Audio Atalante 5

Although I really like my Buchardt S400 MKII, they have usurped by the Atalante 3s for sure.

If I had room for the 5s . . .